High speed steel compositions and articles

ABSTRACT

A new high speed steel composition and article are provided consisting essentially of about 1.20% to 1.40% of carbon, 0.50% maximum manganese, 1.00% maximum silicon, 3.5% to 4.5% chromium, 2.25% to 2.75% vanadium, 5.60% to 6.40% tungsten, 5.60% to 6.40% molybdenum, 5.0% to 7.0% cobalt, 0.02% to 0.08% nitrogen and the balance essentially iron, said high speed steel composition having a ratio of cobalt to equivalent tungsten of about 0.12 to 0.26 and a ratio of vanadium to carbon of 1.7 to 2.1, said composition and article being characterized by extremely high hardness and toughness coupled with resistance to brittleness and breakage.

United States Patent 1 91 Harvey et al.

[ Jan. 7, 1975 HIGH SPEED STEEL COMPOSITIONS AND ARTICLES [75] Inventors: Richard F. Harvey, Orchard Lake;

George E. Moore, Farmington, both of Mich.

[73] Assignee: Moore Production Specialities, Inc.

[22] Filed: Dec. 17, 1973 [21] Appl. No.: 425,569

3,113,862 12/1963 Harvey et a1 75/126 E Primary Examiner-L. Dewayne Rutledge Assistant ExaminerArthur J. Steiner Attorney, Agent, or Firm-*Buell, Blenko & Ziesenheim [57] ABSTRACT A new high speed steel composition and article are provided consisting essentially of about 1.20% to 1.40% of carbon, 0.50% maximum manganese, 1.00% maximum silicon, 3.5% to 4.5% chromium, 2.25% to 2.75% vanadium, 5.60% to 6.40% tungsten, 5.60% to 6.40% molybdenum, 5.0% to 7.0% cobalt, 0.02% to t 0.08% nitrogen and the balance essentially iron, said high speed steel composition having a ratio of cobalt to equivalent tungsten of about 0.12 to 0.26 and a ratio of vanadium to carbon of 1.7 to 2.1, said composition and article being characterized by extremely high hardness and toughness coupled with resistance to brittleness and breakage.

6 Claims, 2 Drawing Figures Nemoto et a1. 75/126 C y PAI'ENTEDJAN H915 3.859.081 sum 10; 2 v

I l l \o '5: Roam/Eu. c ,HARDNass HIGH SPEED STEEL COMPOSITIONS AND ARTICLES This invention relates to high speed steel compositions and articles and more particularly to a new class of high speed steels which combine to a greater degree the desirable properties of high hardness, high resistance to tempering and high toughness.

Furthermore the composition of the present invention involves the moderate use of alloying elements so that there are important additional advantages in cost as well as in savings of strategic-alloying elements as will be explained more fully hereinafter.

The so-called super high speed steels which have advantages over the general purpose high speed steels for many applications, can be classified in four general groups as follows:

5, 8, and 12 percent additions of Cobalt were made to the standard high speed steels starting in the 1920s to result in grades with better red hardness or resistance to tempering. Examples are T4, T5, and T6 high speed steels.

Another improvement involved the high Vanadium high carbon modifications such as M3 and M4 high steels.

A third classification involves the combination of the first two groups. Examples are T15 and M15 high speed steels.

The most recent improvement involves the development of the high carbon high cobalt steels of which M41, M42, M43 and M44 are examples. References to the original work on this group of steels include a report in Metal Progress May 1960 pg. 113 as well as U.S. Pat. No. 3,113,862 issued Dec. 10, 1963 to R. F. Harvey and C. W. Schuck.

In a continuing effort to upgrade high speed steels the present inventors have developed a new class of case hardening high speed steels for specialized applications where the combination of a relatively soft core and hard surface is desirable. This is the subject matter of U.S. Pat. application Ser. No. 884,580 filed July 24, 1969, now abandoned, and U.S. patent application Ser. No. 246,149 filed Apr. 21, 1972.

In view of the foregoing a principal object of the prescarat/65651516fiaviae"5' new high speedsteelcomposition characterized by high hardness, high red hardness, good cutting qualities, and a high degree of toughness as compared with conventional grades.

A related object is to provide for the desirable combination of properties with a moderate alloy content to reduce material costs and to save critical alloys.

In this connection it should be noted that many of the super high speed steels are relatively high in Tungsten and/or Cobalt both of which are in short supply and are imported almost entirely from outside of the United States.

In short the present invention is designed to provide distinct metallurgical improvements over existing high speed steels and also to provide for significant savings in cost and less dependence on foreign sources for strategic alloying elements.

In addition to the obvious cost factor we have found that the overuse of alloys'can have a very detrimental effect on toughness.

For many years the metallurgical literature as well as the various sources for alloys have taught the beneficial use of alloys such as Tungsten, Vanadium, and Cobalt. As a result alloy development has been often based on the premise that if a moderate amount of alloys are good, the addition these alloys in high percentages should provide for better results.

Following this general line of reasoning we find high speed steels and related grades with Tungsten as high as 20%, Vanadium as high as 12% and Cobalt up to about 4%.

Our experience confirms the findings of previous investigators insofar as the beneficial effects of alloys such as Tungsten, Molybdenum, Vanadium and Cobalt is concerned. However we differ in the relative amounts of these alloys which should be used.

What we have found is that with a more balanced composition and with critical alloys and ratios of those alloys held to closely controlled limits, the overall alloy content can be reduced with a marked improvement in the desirable characteristics of high speed steel for most applications.

Based on very extensive experiences and investigations which involves the manufacture of precision metal cutting and forming tools as well as the commercial heat treatment of a wide variety of high speed steels, we find that all of the presently used super high speed steels with 8% or more Cobalt often age harden to develop brittleness which results in breakage and even shattering. It is not uncommon to find these steels to age harden or increase in hardness by one or two points in Rockwell C.

This deficiency is well recognized and has seriously limited the use of the high cobalt high speed steels.

For example M42 is capable of being heat treated to over 68 Rockwell C. However as a practical matter heat treaters are reluctant to accept specifications for maximum hardness on intricate tools due to the danger of cracking either during heat treatment or thereafter due to age hardening. Over the years the hardness to which these steels are heat treated has been reduced in an attempt to avoid breakage and shattering.

A tabulation of the conventional super high speed steels containing Cobalt is included in Table].

Along with the analysis we have tabulated the Vanadium to carbon ratio and the equivalent Tungsten content based on the Tungsten, Molybdenum and Vanadium content. The equivalent Tungsten content is based on the actual Tungsten analysis plus 1.9 times the Molybdenum analysis plus 6.3 times the Vanadium content as developed by H. Wiegand and E. Haberling from Technishe Berichte Jan. 1 1, 1971 Vol B P. 134 to 138.

This tabulation is provided to list the principal super high speed alloys of the prior art and to provide a basis for a better understanding of the development of the composition of the present invention.

Table I Steel C W Cr Va Mo Co V/C Equivalent Tungsten W+l.9 Mo+6.3 Va

T15 1.57 12.5 4.75 5.0 .5 5.0 3.2 44.) M15 1.50 6.5 4.0 5.0 3.5 5.0 3.3 43.7 Rex 73 1.55 10,0 3.75 3.2 5.25 12.0 2.08 40.1

Tab :99301 1 2 Steel. C W Cr Va Mo Co V/C Equivalent Tungsten W1119W+63 Va Rex7l 1.17 10.0 3.75 1.3 5.25 12.0 1.11 28.2 WKE4 1.25 9.0 4.0 3.5 3.5 9.0 2.6 37.1 WKE45 1.4 9.0 4.2 3.5 3.5 12.5 2.5 37.7 M46 125 2.0 4.0 3.2 8.25 8.25 2.5 37.8 M34 .90 1.75 4.0 2.0 8.5 8.25 2.2 30.5 M44 1.15 5.25 4.25 2.25 6.25 12.0 1.9 31.3 M6 .78 4.0 4.0 1.4 5.0 12.0 1.8 22.3 M41 1.10 6.75 4.25 2.0 3.75 5.0 1.8 26.5 M30 .80 1.75 4.0 1.25 8.25 5.0 1.6 25.5 M33 .88 1.75 4.0 1.25 9.5 8.25 1.4 27.7 M43 1.2 2.7 3.75 1.6 8.0 8.2 1.33 27.2 M45 1.25 8.0 4.25 1.6 5.0 5.5 1.28 27.6 M47 1.1 1.6 3.75 1.25 9.5 5.0 1.14 27.4 M42 1.07 1.5 3.75 1.15 9.5 8.0 1.08 26.8 T4 .75 18.0 4.0 1.15 .75 5.0 1.46 26.7 T5 .80 18.5 4.5 2.0 1.0 9.0 2.5 33.0 T6 .80 20.5 4.25 1.6 .6 12.25 2.0 31.6 T8 .80 14.0 4.0 1.15 .75 5.0 1.44 22.7

It will be noted that M42 which has become the most Table II-Continued wldely used of the super high speed steels, has the low- G l R P f d R H enera ange re erre ange eat est Vanadmm to carbon rat1o of 1.08. In our experl %by weight by w ight P65 23 ence th1s1s too low and accounts 1n part at least, for the 2. many deficiencies of this grade. ybde- 5.60/6.40 575/625 5.98

' num It WIll be noted also that most of the super alloys are Cobalt soon-0O 515/615 590 elther h1gh Tungsten base alloys or are based on the M1 25 Nitrogen .02 0 M .03/0 .06

type composition with approximately 89% Molybdenum and about 1%% Tungsten.

Four of the grades M44, M6,.M15 and M41 are Molybdenum Tungsten based steels. However, the M44 and M6 are appreciably higher in Molybdenum than Tungsten and are not balanced compositions within the teachings of this invention. Also M15 and M41 are relatively high in Tungsten and are relatively low in M0- lybdenum as compared with the teachings of the present invention.

We have found that the M3 high speed steel containing approximately equal amounts of Tungsten (6%) and Molybdenum (6%) best combines the desirable properties for cutting and forming applications considering only the non cobalt grades.

In developing a new balanced high speed steel with cobalt, the M3 analysis containing 6% Tungsten and 6% Molybdenum was used as the basis.

In a further development step, we have found that 8% or more cobalt results in unnecessary expense and brittleness. We do find however that at least 5% cobalt is required to obtain high hardnesses in the range of about 70 Rockwell C. Accordingly our improved composition is based on cobalt at about 6%.

Furthermore we have found that the carbon should be about 1.30% and the Vanadium to' Carbon ratio should be about 1.9.

We also find the addition of Nitrogen to be beneficial.

We also find that an increase in the silicon content to about 0.30 to 0.80% is advantageous.

According we have found that the improved steel can be made having the chemical composition shown in Table 11.

The new composition was made in a 1000 lb. commercial heat by powder metallurgy means.

On hardening from 2210F and triple tempering at 1025F a Rockwell C hardness of 69% was obtained.

blg I 151 3 9 a C JIIPQL QIIQf the istance to tempering of the new grade and M41 which has 5% Cobalt and would be in a similar price range to the steel of the present invention.

Table III Comparison of the steel of the present invention and M41 in resistance to tempering.

The results in Table III are included in the tempering curves in FIG. 1.

Curve 1 illustrates the Rockwell C hardness for various tempering temperatures for the steel of the present invention and curve 2 illustrates the Rockwell C hardness for various tempering temperatures for M41.

The peak hardness of Rockwell 68 for the M41 as represented by 3 is obtained with a tempering temperature of about 950 to 1000F.

By comparison the steel of the present invention shows a higher peak hardness Rockwell C 69% as represented by 4 at a higher tempering temperature of 1000 to 1025F.

The higher peak secondary hardness and the higher temperature at which this peak hardness occurs for the steel of the present invention represents a higher degree of red hardness and resistance to softening. This is an important property for high speed steel and is an important factor in the ability of tools to cut and form metals.

An increase in the resistance to tempering constitutes an important step in narrowing the gap between the high speed steels and the cemented carbides.

We have found that it is essential to maintain a balance between the Cobalt content and the equivalent Tungsten content represented by the formula W 1.9 Mo. 63 Va.

In this connection we have plotted in FIG. 2 all of the super high speed steels containing Cobalt which are known together with the steels of the present invention.

The steel of the present invention has a ratio of Cohalt to W 1.9 Mo. 6.3 Va. of 0.189 as illustrated by 5 in FIG. 2.

The Cobalt should preferably be within the limits of 5 to 7 and the equivalent Tungsten content W 1.9 Mo. 6.3 Va. should preferably be within the limits of 30 to 36 as illustrated by area 6, 7, 8, 9 in FIG. 2.

More broadly the Cobalt may be between the limits of 4% to 716% and the equivalent Tungsten content, W 1.9 Mo. 6.3 Va. may be within the limits of 29 to 37 as illustrated by the area 10, 11, 12, and 13 in FIG. 2.

It will be noted that none of the other steels fall within the preferred area 6, 7, 8, and 9 or the broader area 10, 11, 12, and 13 of the present invention.

In general steels higher in Cobalt than the present invention are too brittle and age hardening is often a problem which causes breakage and shattering.

Steels with lower Cobalt than the present invention will not harden to sufficiently high hardnesses.

Also steels with a lower equivalent Tungsten content are found to be relatively brittle and do not harden to the peak hardness of the steel of the present invention. The red hardness of steels in this range is also lower.

Steels having a higher equivalent Tungsten content than the steel of the present invention are over-alloyed and are too costly. Also they are lacking in toughness.

In addition to the Cobalt to equivalent Tungsten ratio we also find the Vanadium to Carbon ratio to be important. This should optionally be about 1.9 and should be v. ..Y",1 1 .1 1.1 imit of 1 173.

' specifications it will be understood that this invention may be otherwise embodied within the scope of the following claims. We claim:

1. An improved high speed steel composition consisting essentially of about 1.20 to 1.40% carbon; 0.50% maximum Manganese; 1.00% maximum Silicon; 3.5 to 4.5% Chromium; 2.25 to 2.75% Vanadium; 5.60 to 6.40% Tungsten; 5.60 to 6.40% Molybdenum; 5.0 to 7.0% Cobalt; and 0.02 to 0.08% Nitrogen with the remainder essentially Iron; said high speed steel composition having a ratio of Cobalt to equivalent Tungsten, of about 0.12 to 0.26% and a Vanadium to Carbon ratio of about 1.7 to 2.1%.

2. A high speed steel composition as claimed in claim 1 in which the Cobalt to equivalent Tungsten ratio is about 0.189.

3. A high speed steel composition as claimed in claim 1 in which the Vanadium to Carbon ratio is about 1.9.

4. A high speed steel composition as claimed in claim 1 in which the Cobalt to equivalent Tungsten ratio is about 0.189 and the Vanadium to Carbon ratio is about 1.9.

5. An improved high speed steel composition consisting essentially of about 1.25 to 1.35% Carbon; 0.20 to 0.40% Manganese; 0.30 to 0.80% Silicon; 3.75 to 4.25% Chromium; 2.35 to 2.65% Vanadium; 5.75 to 6.25% Tungsten; 5.75 to 6.25% Molybdenum; 5.75 to 6.25% Cobalt; and 0.03 to 0.06% Nitrogen with residual elements in normal amounts; said high speed steel composition having a ratio of Cobalt to equivalent Tungsten of about 0.14 to 0.23% and a Vanadium to Carbon ratio of about 1.7 to 2.1%.

6. A high speed steel composition claimed in claim 5 in which the Cobalt to equivalent Tungsten ratio is about 0.189% and also in which the ratio of Vanadium to Carbon is about 1.9%. 

1. AN IMPROVED HIGH SPEED STEEL COMPOSITION CONSISTING ESSENTIALLY OF ABOUT 1.20 TO 1.40% CARBON; 0.50% MAXIMUM MANAGANESE; 1.00% MAXIMUM SILICON; 3.5 TO 4.5% CHROMIUM; 2.25 TO 2.75% VANADIUM; 5.60 TO 6.40% TUNGSTEN; 5.60 TO 6.40% MOLYBDENUM; 5.0 TO 7.0% COBALT; AND 0.02 TO 0.08% NITROGEN WITH THE REMAINDER ESSENTIALLY IRON; SAID HIGH SPEED STEEL COMPOSITION HAVING A RATIO OF COBALT TO EQUIVALENT TUNGSTEN, OF ABOUT 0.12 TO 0.26% AND A VANADIUM TO CARBON RATIO OF ABOUT 1.7 TO 2.1%.
 2. A high speed steel composition as claimed in claim 1 in which the Cobalt to equivalent Tungsten ratio is about 0.189.
 3. A high speed steel composition as claimed in claim 1 in which the Vanadium to Carbon ratio is about 1.9.
 4. A high speed steel composition as claimed in claim 1 in which the Cobalt to equivalent Tungsten ratio is about 0.189 and the Vanadium to Carbon ratio is about 1.9.
 5. An improved high speed steel composition consisting essentially of about 1.25 to 1.35% Carbon; 0.20 to 0.40% Manganese; 0.30 to 0.80% Silicon; 3.75 to 4.25% Chromium; 2.35 to 2.65% Vanadium; 5.75 to 6.25% Tungsten; 5.75 to 6.25% Molybdenum; 5.75 to 6.25% Cobalt; and 0.03 to 0.06% Nitrogen with residual elements in normal amounts; said high speed steel composition having a ratio of Cobalt to equivalent Tungsten of about 0.14 to 0.23% and a Vanadium to Carbon ratio of about 1.7 to 2.1%.
 6. A high speed steel composition claimed in claim 5 in which the Cobalt to equivalent Tungsten ratio is about 0.189% and also in which the ratio of Vanadium to Carbon is about 1.9%. 